Sewage waters a tenth of world's irrigated crops

     12:01 18 August 04

     NewScientist.com news service

     A tenth of the world's irrigated crops - everything from
lettuce and tomatoes to mangoes and coconuts - are watered by
sewage. And much of that sewage is raw and untreated, gushing direct
from sewer pipes into fields at the fringes of the developing world's
great megacities, reveals the first global survey of the hidden
practice of waste-water irrigation.

     And, however much consumers may squirm, farmers like it that
way. Because the stinking, lumpy and pathogen-rich sewage is rich in
nitrates and phosphates that fertilise crops free of charge,
suggests the survey presented at the Stockholm Water Symposium on
Tuesday.

     "Wastewater irrigation is in an institutional no-man's land,"
said Chris Scott of the Sri Lanka-based International Water
Management Institute, co-editor of the study. "Water, health and
agriculture ministries in many countries outlaw the practice, but
refuse to recognise that it is widespread."

     He estimates that 20 million hectares of the world's farms are
irrigated with sewage. A quarter of Pakistan's vegetables, including
salad crops, are grown in sewage effluent, the study found.

     And business is booming. One farmer in the heart of an
un-named West African city grows 12 crops of lettuce a year from his
sewage farm. In many fast-growing megacities, clean water is in
desperately short supply, where sewage is plentiful. And the sewage
pipes keep flowing even in the dry season, when irrigation canals
often dry up.

     Toxic waste

     Farms hooked up to sewage pipes make big profits. The study
found that in parts of Pakistan the price of fields watered by
sewage pipes is twice that of neighbouring fields irrigated with
clean water.

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     In Mexico, Jordan, Israel and Tunisia, sewage is specially
treated to remove pathogens and make it safe for irrigation. But in
India, China and Pakistan, the study found that treatment is rare.
The sewage is added to fields complete with disease-causing
pathogens and toxic waste from industry.

     Sewage is probably the biggest source of water for urban
farming, which provides an estimated one fifth of the world's food,
said Scott. In Hyderabad, the Indian city where he works, "pretty
much a 100 per cent of the crops grown around the city rely on
sewage," he said. "There is no other water available."

     Many consumers would not buy produce at markets if they knew
it had been grown in sewage, he agrees. "Often farmers take the
produce to distant markets, where customers don't know how it is
produced." And farmers themselves run the greatest risks of disease,
he points out.

     But the study concludes that banning the practice is not
usually practicable. "We need to recognise that sewage is a valuable
resource that grows huge amounts of food. So instead we should help
the millions of farmers involved to do it better," said Scott.

     Fred Pearce, Stockholm

     *********

     MikeV